fix: Avoid using lsof -Q which is only available from lsof 4.95.0

(Debian 11 (oldstable) and Ubuntu 22.04 LTS both have lsof 4.93.2.)

The only drawback we could expect is generating a nonzero exit code,
but the current implementation with Unix.open_process_in works as is.

src/server/learnocaml_server.ml

@@ -718,7 +718,7 @@ let launch () =
 
 let check_running () =
   try
-    let ic = Printf.ksprintf Unix.open_process_in "lsof -Qti tcp:%d -s tcp:LISTEN" !port in
+    let ic = Printf.ksprintf Unix.open_process_in "lsof -ti tcp:%d -s tcp:LISTEN" !port in
     let pid = match input_line ic with
       | "" -> None
       | s -> int_of_string_opt s